Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas channel for supplying a fuel gas such as a hydrogen-gas to the anode and an oxygen-containing gas channel for supplying an oxygen-containing gas such as the air to the cathode are formed along surfaces of the separators.
For example, in a flat stack fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-120589, as shown in FIG. 13, a separator 1 stacked on a power generation cell (not shown) is provided. The separator 1 is formed by connecting left and right manifold parts 2a and a part 2b at the center where the power generation cell is provided, by joint parts 2c. The joint parts 2c have elasticity.
The manifold parts 2a has gas holes 3, 4. One gas hole 3 is connected a fuel gas channel 3a, and the other gas hole 4 is connected to an oxygen-containing gas channel 4a. The fuel gas channel 3a and the oxygen-containing gas channel 4a extend in a spiral pattern into the part 2b, and are opened to a fuel electrode current collector and an air electrode current collector, respectively, at positions near the center of the part 2b. 
In the above conventional technique, it is desired that the manifold parts 2a are sealed suitably, and the adjacent part 2b suitably contact the adjacent component. In particular, it is necessary to reliably prevent the leakage of the fuel gas or the oxygen-containing gas. In order to improve the sealing performance in the manifold parts 2a, normally, a large sealing load is applied to the manifold parts 2a. 
However, since the joint parts 2c are formed around the part 2b where power generation is performed, when the large load is applied to the manifold parts 2a, the joint parts 2c likely to tightly contact each other. Thus, the exhaust gas is not smoothly discharged from the outer circumferential portion of the part 2b. Accordingly, temperature gradient is generated in the electrolyte electrode assemblies. As a result, the electrolyte electrode assemblies are damaged or degraded, and do not function properly. Therefore, power generation may not be performed efficiently and reliably.